1. Field of the Invention
The present invention relates to a process for the nitration of phenolic compounds.
2. Description of the Prior Art
It is known to this art to nitrate very many compounds, typically by using a sulfuric acid/nitric acid admixture, or also by using a dilute or concentrated solution of nitric acid. Compare, for example, "Nitration and Aromatic Reactivity" by J. G. Hoggett and R. B. Moodie (1971) published by Cambridge University Press and "Aromatic Nitration" by K. Schofield (1980) published by Cambridge University Press.
Nitrophenols (principally the ortho and para isomers) are generally prepared by nitration of phenol with nitric acid and in a sulfuric medium. See, for example, the paper by R. B. Moodie in "Journal of Chemical Society, Perkin Trans.", II, 1985, page 467.
The nitration of phenols is most frequently carried out in a sulfuric medium and rarely in an organic medium.
During the preparation of nitrophenols, certain by-products of oxidation, such as, in particular, benzoquinone derivatives and derivatives of high molecular weight originating from the condensation of several aromatic molecules, are typically observed, and this necessitates carrying out awkward purification operations.